Public health and social measures during health emergencies such as the COVID‐19 pandemic: An initial framework to conceptualize and classify measures

Abstract Background Public health and social measures (PHSM) intend to reduce the transmission of infectious diseases and to reduce the burden on health systems, economies and societies. During the COVID‐19 pandemic, PHSM have been selected, combined and implemented in a variable manner and inconsistently categorized in policy trackers. This paper presents an initial conceptual framework depicting how PHSM operate in a complex system, enabling a wide‐reaching description of these measures and their intended and unintended outcomes. Methods In a multi‐stage development process, we combined (i) a complexity perspective and systems thinking; (ii) literature on existing COVID‐19 PHSM frameworks, taxonomies and policy trackers; (iii) expert input and (iv) application to school and international travel measures. Results The initial framework reflects our current understanding of how PHSM are intended to achieve transmission‐related outcomes in a complex system, offering visualizations, definitions and worked examples. First, PHSM operate through two basic mechanisms, that is, reducing contacts and/or making contacts safer. Second, PHSM are defined not only by the measures themselves but by their stringency and application to specific populations and settings. Third, PHSM are critically influenced by contextual factors. The framework provides a tool for structured thinking and further development, rather than a ready‐to‐use tool for practice. Conclusions This conceptual framework seeks to facilitate coordinated, interdisciplinary research on PHSM effectiveness, impact and implementation; enable consistent, coherent PHSM monitoring and evaluation; and contribute to evidence‐informed decision‐making on PHSM implementation, adaptation and de‐implementation. We expect this framework to be modified and refined over time.


| INTRODUCTION
At the beginning of the COVID-19 pandemic, many of the characteristics of the novel virus SARS-CoV-2 were unknown, and neither vaccines nor effective pharmaceutical treatments were available. This placed public health and social measures (PHSM) in the spotlight then and throughout the pandemic. 1 Although the importance of PHSM is recognized globally, many questions remain.
PHSM-often also referred to as non-pharmacological interven-

| Objective of this paper
This paper presents an initial conceptual framework of PHSM that This framework is conceptual, not operational. It thus provides a tool for structured thinking, rather than a ready-to-use tool for practice. It is, however, intended as the starting point for developing specific tools that meet the needs of distinct user groups and institutions, notably those conducting PHSM research, tracking PHSM and making decisions about PHSM. This work has been undertaken to support the WHO PHSM initiative to measure the effectiveness and broader impact of PHSM during health emergencies, which seeks to strengthen the global evidence base to inform the development of actionable tools for decision-makers. 5 The conceptual model will be further developed through extensive expert consultations.

| METHODS
Our approach to developing the conceptual framework of PHSM was informed by a system-based logic model template 6 and a staged approach to logic modelling. 7 The resulting initial framework will be further advanced.
The multi-stage development process used (i) a theoretical perspective recognizing PHSM as 'complex interventions in complex systems' 2 ; (ii) literature on existing COVID-19 PHSM frameworks, taxonomies and policy trackers (subsequently referred to as frameworks); (iii) WHO expertise; and (iv) application to two distinct settings. A graphical overview of this development process can be found in Figure S1.
The development and iterative refinement of the framework categories was facilitated through regular meetings among the entire author team, with results presented through visualizations using an online whiteboard (MIRO). 8 We held author meetings to work on the 'big picture', integrate insights gained across the different inputs and discuss and resolve any conceptual inconsistencies; we also held smaller team meetings to address specific components or aspects.
Informed by a complexity perspective and systems thinking, we used selected additional frameworks to advance specific components, and inform broader decision-making criteria regarding PHSM, especially the Context and Implementation of Complex Interventions (CICI) framework, 9 the CONSEQUENT framework for unintended consequences of public health interventions, 10 the Nuffield Intervention Ladder 11 and the WHO-INTEGRATE evidence-to-decision framework. 12 To ensure that the conceptual framework builds on existing literature on COVID PHSM, we searched the websites of selected national and international health organizations, conducted targeted literature searches in Pubmed (using combinations of search terms related to COVID-19 and PHSM, as well as search terms related to taxonomy, conceptual framework and policy tracker) and consulted with WHO. We mapped the identified frameworks by (i) extracting key elements and (ii) (re)coding these elements into a priori defined classes based on the WHO taxonomy and glossary of PHSM 4 as well as emerging inductive classes for elements that did not fit the predefined classes.
To identify potential missing elements, ensure fit with the objectives and activities of the WHO PHSM initiative and make the framework understandable and appropriate to users, we engaged with members of the WHO PHSM secretariat and the Methods Working Group of the WHO PHSM Initiative and obtained feedback from the WHO PHSM steering group, including staff members from all six WHO regional offices and across a broad range of departments and disciplinary perspectives.
To ensure its face validity and further advance categories and their components, the author team applied the model to develop classifications of PHSM in two settings, namely, in schools and at points of entry to a country (airports, ports and ground crossings), drawing on existing COVID PHSM frameworks, systematic reviews 13,14 and guidelines, 15 as well as lived experience.

| Mapping and coding of existing COVID PHSM frameworks
We found 14 frameworks of COVID PHSM, including some referred to by the developers as taxonomies and policy trackers. 3,4,13,14,[16][17][18][19][20][21][22][23][24][25] Key elements extracted from these frameworks (see Supporting Information) provided a starting point for developing the different categories of our framework and the specific components within these categories. We identified four significant challenges with the identified frameworks. First, the majority lacked a conceptual foundation and thus resembled a 'laundry list of measures' rather than a coherent and consistent classification system. They also had limited conceptual clarity with individual categories not being mutually exclusive, showed varying degrees of granularity and largely did not clearly consider mechanisms and contexts (i.e., what, how, why and for whom).
Second, a complexity perspective and systems thinking was lacking, with no attention paid to interactions across different categories or components or to the positive or negative consequences of measures. Third, the identified frameworks were poorly equipped to address the dynamic nature of a pandemic and rarely took into account adaptation or de-implementation of measures. Fourth, most lacked definitions of the measures and other relevant aspects (e.g., stringency), as well as explicit links to decision-making, rendering many of them difficult to operationalize in a consistent manner.
3.2 | The initial conceptual framework Figure 1 presents the structure of the initial conceptual framework.
The framework consists of the categories objective, population, setting, measures, stringency and outcomes; a central hub integrates all categories and ensures various critical functions during a health emergency. Each of these categories includes specific components; whereas for some of the categories, the constituent components are well-elaborated, and the components for the other categories are yet-to-be developed through distinct activities of the WHO PHSM initiative. In its structure, the framework thus follows the 'Russian dolls principle'; that is, it includes a high level of abstraction to maintain simplicity and ensure a 'big picture view', but all categories can be further unpacked. Figure 2 presents the initial framework, unpacking the categories objectives, measures, stringency and outcomes. Figure   with other individuals; wearing a mask when attending a meeting or going to a supermarket serves to make contacts with others safer. Some PHSM can do both, depending on the perspective adopted. For example, testing can serve to reduce contacts (e.g., restricting hospital access to visitors with an up-to-date negative test will reduce the number of visitors); it also serves to make contacts between F I G U R E 2 An initial conceptual framework of public health and social measures during health emergencies: framework categories and their components.
F I G U R E 3 Placement of exemplary public health and social measures (PHSM) according to intervention mechanism and on a spectrum from individual to population agency.
individuals safer (i.e., contacts in the hospital will only take place between individuals who tested negative). Figure 3 presents widely used categories of PHSM according to their basic mechanism. They fall on a spectrum from measures targeting individuals (e.g., hand hygiene) to population subgroups (e.g., workplace ventilation) to whole populations (e.g., stay-at-home orders). Many PHSM can be conceived as individual-level measures (e.g., mask wearing to selfprotect or to protect others) but show a substantial 'herd effect' when widely used at a community and population level (e.g., widespread mask wearing on public transport).

| Measures
The framework contains two sets of measures: those that reduce transmission and those that address the consequences of transmission-related measures (yet to be developed). As described above, for measures reducing transmission, we distinguish between those reducing contacts and those seeking to make contacts safer.
The former includes response measures, measures targeting services, social interactions and movement; the latter includes physical environment and individual protection measures. Surveillance measures, depending on the perspective adopted, make use of both intervention mechanisms (see Figure 3). Definitions for each measure are presented in Table 1, accompanied by specific examples.

| Stringency
This category describes the level of strictness with which measures are implemented; it thus primarily refers to the vigour of government action and relates to the extent of individual agency and autonomy.
It distinguishes between enabling uptake-empowering and supporting people with regard to certain activities/behaviours by informing choice or guiding choice-and mandating uptake-officially requiring people to take up certain activities/behaviours by restricting choice or eliminating choice. It retains the notion of degree of intrusiveness described in the Nuffield intervention ladder 11 but compresses its multiple rungs into fewer levels. Importantly, stringency relates to the nature of measures rather than to the means by which they are enacted (e.g., fines to make people obey a mandate).

| Outcomes
These comprise those directly related to transmission (i.e., cases, hospitalizations, morbidity during and/or post-infection and deaths) as well as less direct and broader unintended or intended consequences for health and society, informed by the CONSEQUENT framework. 10 These consequences may be positive (co-benefits, e.g., reduced air pollution due to mobility restrictions) or negative (adverse effects, e.g., increased socio-economic inequality in educational outcomes due to school closures); these could also be described as spillover effects of an intervention.

| Setting
This category refers to the specific physical location, in which the intervention is put into practice and interacts with context and implementation. 9 It comprises 13 specific settings that were drawn up from settings identified in existing COVID PHSM frameworks and subsequently clustered, summarized and complemented by the literature or experts.

| Population
This category defines populations according to (i) their susceptibility to infection (e.g., immune status due to prior infection or vaccination) and/or their susceptibility to severe health consequences (e.g., due to age or pre-existing conditions), (ii) their exposure to infection (e.g. due to living or working conditions) and/or (iii) their susceptibility to and/or experience of negative consequences (e.g., as a result of lower socioeconomic status).

Services
Measures to modify services comprise adaptation, cancellation and/or modified timing of services or activities to prevent transmission of an infectious agent.
Closure of schools, closure of non-essential businesses

Social interactions
Measures to modify social interactions adapt the ways in which individuals and groups of people interact with each other.

Cancellation of large gatherings Movement
Measures to modify movement adapt the ways in which individuals or groups of people move within and between specific settings and within or across national borders.

Suspension of flights between countries, domestic mobility restrictions
Measures making contacts safer Measures making contacts safer reduce the probability of transmission when people meet in-person/faceto-face. These comprise physical environment measures as well as individual protection measures.

Physical environment
Physical environment measures operate by directly reducing the exposure of individuals to an infectious agent and/or by enabling healthy behaviours of individuals. They adapt the physical infrastructure ('hardware') through modifications to or re-purposing of the infrastructure and also comprise the appropriate maintenance of existing or newly set up infrastructure.

Physical barriers, ventilation, air purifier, soap and disinfectant provision
Individual protection Individual protection measures comprise personal protective equipment as well as specific behaviours that reduce the risk of individuals transmitting and/or contracting an infectious agent.

Both Surveillance
Surveillance measures test or screen individuals and/or groups of people. These make contacts safer by identifying potentially infected and/or infectious individuals and, at the same time, reduce contacts between infected individuals and individuals at risk of being infected. They comprise strategies to test symptomatic individuals or contact persons, to screen an asymptomatic group of people (routinely or in a time-limited, short-duration manner in response to an outbreak) or to routinely test a fraction of a certain population to identify potential outbreaks.
Surveillance testing, diagnostic testing, routine screening

| Applying the initial conceptual framework to measures for schools and international travel
We applied the framework to two specific settings: schools and points of entry to a country (airports, ports and ground crossings). To For international travel, the aim of the measures is to reduce the risk of transmission through or during travel between countries via air, land or sea, thereby avoiding or delaying importations/exportations of cases. Stringency refers to the ability of individuals or groups to freely travel between countries, as well as to freely use a range of services (e.g., meals) and opportunities (e.g., having accompanying relatives at the departure/arrival areas) during travel and at the point of entry. These applications showed that the conceptualization worked well. It surfaced some conceptual challenges that were subsequently resolved. The applications also provided input towards refining definitions for distinct measures and levels of stringency.

Stringency Definition Examples
Enabling uptake Enabling uptake serves to empower and support people with regards to certain activities/behaviours.

Informing choice
Inform choice regarding certain activities/behaviours and/or recommend a given activity/behaviour Providing information to students and school staff on where to get tested

Guiding choice
Guide choice regarding certain activities/behaviours through enabling measures and/or financial and non-financial incentives or disincentives Providing tests to students and school staff free of charge

Mandating uptake
Mandating uptake officially requires people to take up certain activities/behaviours.

Restricting choice
Restrict choice regarding certain activities/behaviours thereby strongly promoting these activities/ behaviours but offering limited alternative activities/behaviours Allowing access to school premises to tested or vaccinated school staff

Eliminating choice
Eliminate choice regarding certain activities/behaviours thereby determining people's activities/behaviours and offering no alternative activities/behaviours (i.e., any alternative activities/behaviours are associated with extremely high costs) Allowing access to school premises to school staff with proof of a negative test only operate through two basic mechanisms to reduce human-to-human transmission, that is, reducing contacts and/or making contacts safer.
Second, specific PHSM are not only defined by the measures themselves-they depend on their interplay with stringency and the populations and settings targeted. Third, PHSM-the choice of distinct measures and levels of stringency, as well as the resulting benefitharm-balance-are shown to be influenced by a broad range of contextual factors. This framework is a basis for others to use and, in doing so, to suggest modifications and refinements.

| Strengths and limitations
To our knowledge, this conceptual framework represents the only available PHSM framework that has used an explicit and robust devel- Widening the evaluation of the framework's range of applicability will provide information about its generalizability across populations, settings and type of health threat.  (Table S1) and international travel (Table S2)